As ignition means for internal combustion engines of motor vehicles, there are known spark plugs which have a spark discharge gap formed by opposing a center electrode and a ground electrode. Such spark plugs discharge a spark in the spark discharge gap, thereby igniting an air-fuel mixture in a combustion chamber of an internal combustion engine.
In the combustion chamber, there is formed a flow of the air-fuel mixture, such as a swirl flow or tumble flow. With the flow of the air-fuel mixture moderately flowing also in the spark discharge gap, it is possible to ensure the ignition performance.
To this end, there has been disclosed a spark plug which has a protruding member provided on a distal end portion of a housing so as to guide the flow of the air-fuel mixture in the combustion chamber to the spark discharge gap (see Patent Document 1).